2013 US Open - Day 12

Victoria Azarenka of Belarus plays a forehand during her women's singles semifinal match against Flavia Pennetta of Italy on Day Twelve of the 2013 US Open at USTA Billie Jean King National Tennis Center on September 6, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo: Getty Images)

Serena Williams of United States of America serves during her women's singles semifinal match against Na Li of China on Day Twelve of the 2013 US Open at USTA Billie Jean King National Tennis Center on September 6, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo: Getty Images)

Serena Williams of United States of America celebrates a point during her women's singles semifinal match against Na Li of China on Day Twelve of the 2013 US Open at USTA Billie Jean King National Tennis Center on September 6, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo: Getty Images)

Serena Williams of United States of America shakes hands at the net with Na Li of China after their women's singles semifinal match on Day Twelve of the 2013 US Open at USTA Billie Jean King National Tennis Center on September 6, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo: Getty Images)

Serena Williams of United States of America celebrates a point during her women's singles semifinal match against Na Li of China on Day Twelve of the 2013 US Open at USTA Billie Jean King National Tennis Center on September 6, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo: Getty Images)

Serena Williams of United States of America reacts during her women's singles semifinal match against Na Li of China on Day Twelve of the 2013 US Open at the USTA Billie Jean King National Tennis Center on September 6, 2013 in New York City. (Photo: Getty Images) Serena Williams of United States of America plays a backhand during her women's singles semifinal match against Na Li of China on Day Twelve of the 2013 US Open at USTA Billie Jean King National Tennis Center on September 6, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo: Getty Images) Na Li of China plays a forehand during her women's singles semifinal match against Serena Williams of United States of America on Day Twelve of the 2013 US Open at USTA Billie Jean King National Tennis Center on September 6, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo: Getty Images) Serena Williams of United States of America plays a forehand during her women's singles semifinal match against Na Li of China on Day Twelve of the 2013 US Open at USTA Billie Jean King National Tennis Center on September 6, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo: Getty Images) Flavia Pennetta of Italy plays a forehand during her women's singles semifinal match against Victoria Azarenka of Belarus on Day Twelve of the 2013 US Open at USTA Billie Jean King National Tennis Center on September 6, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo: Getty Images) Victoria Azarenka of Belarus plays a forehand during her women's singles semifinal match against Flavia Pennetta of Italy on Day Twelve of the 2013 US Open at the USTA Billie Jean King National Tennis Center on September 6, 2013 in New York City. (Photo: Getty Images) Victoria Azarenka of Belarus plays a forehand during her women's singles semifinal match against Flavia Pennetta of Italy on Day Twelve of the 2013 US Open at USTA Billie Jean King National Tennis Center on September 6, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo: Getty Images)

Victoria Azarenka of Belarus celebrates winning her women's singles semifinal match against Flavia Pennetta of Italy on Day Twelve of the 2013 US Open at the USTA Billie Jean King National Tennis Center on September 6, 2013 in New York City. (Photo: Getty Images)

Victoria Azarenka of Belarus kisses Flavia Pennetta of Italy at the net after their women's singles semifinal match on Day Twelve of the 2013 US Open at USTA Billie Jean King National Tennis Center on September 6, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo: Getty Images) Victoria Azarenka of Belarus celebrates winning her women's singles semifinal match against Flavia Pennetta of Italy on Day Twelve of the 2013 US Open at USTA Billie Jean King National Tennis Center on September 6, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo: Getty Images) Flavia Pennetta of Italy plays a forehand during her women's singles semifinal match against Victoria Azarenka of Belarus on Day Twelve of the 2013 US Open at USTA Billie Jean King National Tennis Center on September 6, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo: Getty Images) Flavia Pennetta of Italy celebrates a point during her women's singles semifinal match against Victoria Azarenka of Belarus on Day Twelve of the 2013 US Open at USTA Billie Jean King National Tennis Center on September 6, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo: Getty Images)